Researchers have been studying toll-receptors for decades, revealing functions in immune defence developmental biology. Now, a research team from Kiel University says reporting that toll-receptors have primarily served to identify germs and to control bacterial colonization of organisms – typical immune defense functions.

Toll receptors exist in many animal species as well as humans. Cnidarians are convenient research subjects because they live in plain aquaria, have a simple genome and can be examined easily in experiments. They also live in association with few types of bacteria compared to humans.

"Studying cnidarians, we were able to show that toll-receptors have been involved in immune defence already in this evolutionarily old phylum and that cnidarians can therefore serve as model organisms for human immunology research,” says Thomas Bosch from the Zoological Institute of Kiel University who led the project.

In 1985, toll-receptors were first discovered as a key factor in embryonic development of the fruit fly (Drosophila melanogaster). For these findings, Christiane Nüsslein-Volhard, Edward Lewis und Eric Wieschaus were awarded the 1995 Nobel Prize for medicine. Then researchers discovered a new function, that the toll-receptor helped to identify germs in both the fruit fly as well vertebrate animals, biologists Jules Hoffmann, Bruce Beutler and Ralph Steinmann received the Novel Prize for medicine in 2011.

Scientifically, the subsequent question became 'Which function – regulation of embryonic development or immune defense – was first in evolution?' Researchers studied the function of toll receptors in cnidarians, an evolutionarily very old group existing for more than 600 million years. The scientists compared morbidity and bacterial colonization of regular and genetically modified polyps of the genus Hydra.

The study resulted in strong evidence for immunobiological functioning of the toll-receptors, implying that developmental functions of the toll-receptor are characteristic of insects, which are evolutionarily much younger.Citation: Sören Franzenburg,Sebastian Fraune, Sven Künzel, John F. Baines, Tomislav Domazet-Loso and Thomas C. G. Bosch, " MyD88-deficient Hydra reveal an ancient function of TLR signaling in sensing bacterial colonizers", Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1213110109